## How Oximeter measures Pulse Rate & Oxygen level in your Blood

A Pulse Oximeter is as small clip like device that measures pulse rate & oxygen level (SPO2) in your blood by non-invasive method .

You should know that a normal resting pulse rate is in between 60 to 100 BPM (beats per minute) and normal oxygen level (SPO2) between 95% to 100% .

As we know that we need oxygen for survival . Oxygen enter our lungs and pass on into the blood . The way oxygen is carried in our blood by means of Hemoglobin . The Hemoglobin (Hb) with oxygen called “ oxy Hb “ and without oxygen called “deoxy Hb” . Oxy Hb and deoxy Hb absorbs infrared & red light differently . Oxy Hb absorb more infrared light and deoxy Hb will absorb more red light .

How it Works :

A pulse oximeter uses a pair of light (infrared & red) of high intensity from LED (Light Emitting Diode)to measure oxygen saturation level in your blood .

The device has a light source and light detector . If a finger is placed between light source and detector , the light has to pass through the finger to reach the detector .

According to law in Physics “The amount of light absorbed is proportional to the concentration of light absorbing substance ” .

As Hemoglobin (Hb) absorbs light . “The amount of light absorbed is proportional to concentration of Hb in blood vessel “ .

As Oximeter detects how much light has been absorbed and how much reaches the detector . In this way oximeter measures the oxygen level in the blood .

In covid-19 pandemic everyone should keep pulse oximeter in his house . This device is small & also not so costly . You may purchase it from any medical store or online store .

## How Video game can improve your memory and Concentration

As we all know that gaming is essential for physical & mental fitness .

In this article we are talking about brain train game . The question arises  always in our mind that , can brain train game improves our memory & Concentration ? The answer is Yes .

It has to be found by study that brain train game improves short term memory , long term memory , response time and logical thinking skills .If a person would like to give workout to his brain , it may improve mental focus & fitness . It has to be found by neurobiologist in his study gaming can improve memory test score . In his study on two groups playing video games , one group that played in 2-D environment and other in 3-D environment . After playing 30 minutes per day for two weeks , the participants were given memory test , the participants those in 3-D group significantly improve their memory test score as compared to 2-D group . There are many games by which you may improve your skills such as reading , writing , speaking etc. You may also customize according to your choice and also track your progress to see how your skills are improving .

### CHESS :

If you want to improve your memory & concentration consider all time classic “CHESS” . It has to be found by study that regular CHESS player or expert have better memory & concentration . You may also serve social activity by playing Chess with your friend , family & colleague .

In other way you may also prefer to play on your Mobile Phones , tablets or PC .  In this way it will provide you virtual Competitors and you can challenge your mind . Playing more focussed chess also improves your logical thinking .

### VIDEO GAME:

Video games are another better options for improving memory & concentration . It has to be found by study that video games which are based on playing & skillful thinking helps to improve the brain function .

Video game can also bridge the gap between adult & children by playing game together and also builds up deeper relationships . It has to be found that video game player also improves their several types of attention such as sustained attention , selective attention etc.

RELIEF PHYSICAL PAIN  :  It has to be found by study that video game may also relief physical & mental pain . Patient get relief from pain by engaging themselves with video game .

REDUCING DEPRESSION & STRESS : Video game may also helps in reducing stress for those students who suffering  from depression & stress .

IMPROVE DECISION MAKING CAPACITY : On playing games , gamer has to take second decision at a certain instant of time by doing this he can improve their decision making capability .

“  One should always keep in mind that games are for Refreshment for their mind , body & soul “

## Electromagnets & Permanent magnets

### Electromagnets

They are normally used for the purpose of lifting ferromagnetic substance.

Properties of the material of an electromagnet :

(1)  The material should have low retentivity so that it gets demagnetised easily.

(2)  For the electromagnet to be very strong, it should have a high value of saturation magnetisation.

(3)  It should have low coercivity .

(4)  Hysteresis loss should be small. It should not be heated up during magnetisation and demagnetisation.

The above-mentioned properties are reasonably met with soft iron and so soft iron is usually preferred for an electromagnet.

### Permanent magnets

Normally used in measuring instruments.

Properties of the material of a permanent magnet :

(1)  It should have high retentivity so that it remains magnetised in the absence of the magnetising field.

(2)  It should have high saturation magnetisation.

(3)  It should have high coercivity so that it does not get demagnetised easily.

Note:Compared to soft iron, steel has got low retentivity. Even then steel is preferred for a permanent magnet as it has got high coercivity.

### Trasformer cores

As the materials used for making transformer cores are subjected to many cyclic changes per second, so they are preferred to have low hysteresis loss. Moreover magnetic field B should be large. As soft iron shows these properties, hence it is always preferred to develop transformer cores.

## Eddy current & its applications

Eddy Currents :
Eddy currents are the currents induced in the body of a conductor when the amount of magnetic   flux linked with it changes. The experimental concept was given by Focault and hence they are also named as Focault currents.

Special points:
(1) These currents are produced in metal bodies

(a)They are placed in a time varying magnetic  field .

(b)They move in a magnetic field such that their flux through them changes or they cut away magnetic field lines .

(2) These currents are produced only in closed path within the entire volume of metal body or surface area of metal body. Therefore their measurement is impossible.

(3) These “circulatory” currents are always produced in planes perpendicular to magnetic lines of force.

(4) The resistance of bulk conductor is usually low, eddy currents often have large magnitudes and heat up the conductor. That’s why these are sometimes undesirable.

(5) By ‘ Laminations ’ , slotting process, the resistance path for circulation of eddies increases, resulting in to weakening them and also reducing losses caused by them. Slots and laminations intercept the conducting paths and decrease the magnitude of eddy currents. That’s why a laminated metal core is always preferred to be used in an appliance like dynamo, transformer, choke will etc.

Special Examples on eddy currents

(1)If a metal piece and a stone are dropped from the same height near earth’s surface, then eddy currents are produced in the falling metal piece due to earth’s magnetic field which opposes its motion. So the metal piece falls with acceleration a < g. Whereas no eddies are produced in stone, so it will fall with acceleration due to gravity. So the stone will reach the earth earlier.

For any time interval : hmetal > Hnonmetal

For any given height   : tmetal > tnonmetal

(2)If a metallic plate is below an oscillating magnet, then magnet stops soon because eddy currents are produced in the plate which opposes the motion of magnet. This is the basis of electromagnetic damping.

(3)  If a bar magnet is falling vertically through the hollow region of a long vertical copper tube, then the magnetic flux linked with the copper tube (due to ‘non-uniform’ magnetic field of magnet) changes and eddy currents are generated in the body of the tube.
By Lenz’s law the eddy currents oppose the falling of the magnet which therefore experiences a retarding force .The retarding force increases with increasing velocity of the magnet and finally equals the weight of the magnet. The magnet then attains a constant final terminal velocity i.e. magnet ultimately falls with zero acceleration in the tube.

On heating the tube its resistance will increase and so the eddy currents will become feeble, resulting in an increase in the terminal velocity of the magnet.

Applications of eddy currents

(i)    Induction furnace (heating effect of eddy current)

(iii)  Electric brakes

(iv) Diathermy ( Strong 50 MHz A.C. passed through human body, also called deep heat treatment )

(v)  Induction motor

(vi) Car-speedometer

(vii)Energy meter

## Thomson Mass Spectrograph

Thomson Mass Spectrograph which is used to measure atomic masses of various isotopes in a gas :

Thomson mass spectrograph is used to measure atomic masses of various isotopes in a gas. This is done by measuring q/m of singly ionized positive ions of the gas. The positive ions are produced in the bulb at the left-hand side. These ions are accelerated towards cylindrical cathode C.

Some of the positive ions pass through the fine hole in the cathode. This fine ray of positive ions is subject to electric field E and magnetic field B and then allowed to strike a fluorescent screen or photographic plate placed just before the screen (not shown in figure). The positive ions produced near the anode are accelerated through a greater distance and thus have more kinetic energy and velocity. The different positive ions have different speeds. It can be shown that all positive ions having the same q/m, fall on the screen or photographic plate forming a parabolic trace. By changing the direction of B the other side of the parabola can be obtained.
It is found that separate isotopes forms separate parabola. Thus the number of parabolas (figure) given the number of isotopes in the gas taken in the bulb. Some ions after coming out of the cathode get neutralize and continue to move in a straight line. The impinge at the vertex of the parabola, forming a dark spot on the photographic plate.

The electric field and magnetic field are parallel to each other. However, the electric force and the magnetic force are perpendicular to each other. The deflection (upwards) due to the electric field alone as observed on the screen is .

$\displaystyle Y = \frac{q E L D}{m u^2}$

While the deflection (side ways) due to the magnetic field alone is

$\displaystyle X = \frac{q B L D}{m u}$

Eliminating u, we notice that when both E and B are present, then X – Y coordinates of the deflection are related by

$\displaystyle X^2 = \frac{B^2 L D}{E} (\frac{q}{m} ) Y$

For a given spectrograph B , L , D , E are constants , then

$\displaystyle X^2 = K (\frac{q}{m}) Y$

Note :

(1)   Thus all positive ions having charge to mass ratio (q/m) lie on a parabola. Higher is the velocity, lower is the value of Y and X. In principle only those positive ions for which velocity is infinite can reach the origin O.

(2)   Thus, infact, the trace does not extend upto origin O (vertex of the parabola). Since the highest velocity positive ions are those which originate near anode, the parabola’s lower end is due to high velocity ions, low velocity ions are far away from the vertex on the parabolic trace.

(3)   To determine m1/m2 ratio of isotopic masses, one draws a horizontal line on the parabolic trace (see figure). Thus Y is same for the two traces. Then the ratio m1/m2 is found to be (use X2 = K (q/m) Y).

$\displaystyle \frac{m_1}{m_2} = \frac{(AB)^2}{(CD)^2}$

where AB = 2X2 and CD = 2X1 in the figure. The heavier isotope lie on the inner parabolic trace while the lighter isotope is on the outer parabolic trace. The q/m is large for the outer parabola (m small) while q/m is small for the inner parabola. Thomson, using this spectrograph, discovered the isotopes of the neon.

Drawbacks:

(i) The resolving power of Thomson spectrograph is poor.

(ii) The parabolas are thick (diffused) as such it is difficult to accurately measure the distances AB and CD.

(iii) Since the positive ions are spread over a parabolic trace, the intensity is weak as such isotope having a little abundance may not be able to form a detectable parabolic trace.

(iv) If the positive ions before striking the screen (photographic plate) collide with atoms of the gas in the spectrograph tube, they will diffuse the parabolic trace and may also give rise to false parabolic traces.

(v) The relative abundance of the isotopes is estimated by intensity of the parabolic traces.